The present invention relates to a driving system of an AC motor, and more particularly to a system which can realize a high-performance motor control without using a sensor which detects an electrical angle position of an AC motor.
As methods for controlling a synchronous motor without detecting an electrical angle position, methods which are described in Japanese Patent Laid-Open No. 245981/1995 (referred to as xe2x80x9cliterature 1xe2x80x9d hereinafter), Japanese Patent Laid-Open No. 177788/1995 (referred to as xe2x80x9cliterature 2xe2x80x9dhereinafter), xe2x80x9cMethod for estimating positions of magnetic poles of a PM motor which focuses on a magnetically non-linear electric current distortionxe2x80x9d, Japan Electric Society, Industrial Application Section, Nationwide Convention, No.191, 1999 (referred to as xe2x80x9cliterature 3xe2x80x9d hereinafter) and the like have been known. Methods described in all these literatures relate to the method for estimating magnetic poles in the inside of a synchronous motor.
The technique described in the literature 1 performs the estimation of positions of magnetic poles by making use of the electrically salient characteristics of a permanent magnet type synchronous motor (PM motor). In this technique, an alternating magnetic field is generated on an estimated magnetic pole axis (dc axis) of the PM motor, an AC current (or an AC voltage) having a component in an axis which intersects the estimated magnetic pole axis (qc axis) is detected, and the positions of magnetic poles in the inside of the motor are calculated by estimation based on the detected AC current. When there is an error between the actual magnetic pole axis and the estimated magnetic flux axis, the feature that the interference term of the inductance is present between the dc axis and the qc axis is used. However, to extract the AC current (voltage) component, the Fourier series (the Fourier expansion) or a band pass filter is used.
The technique described in the literature 2 performs the estimation calculation of the positions of the magnetic poles using the electrically salient characteristics and the magnetic saturation characteristics of the PM motor. The estimation algorithm is divided in two steps consisting of a step 1 and a step 2, wherein the estimation of the positions of the magnetic poles is performed using the electrically salient characteristics of the PM motor in the step 1 and the change of inductance due to the magnetic saturation is measured and the polarities of the magnetic poles are discriminated in the step 2.
The technique described in the literature 3 calculates the positions of the magnetic poles by estimation using the magnetic saturation characteristics of the PM motor. In this technique, a sinusoidal voltage having high frequency is applied to the PM motor and the current waveform generated according to such an application of voltage is subjected to a frequency analysis thus calculating the polarities of the magnetic poles and the positions of the magnetic poles by estimation based on the phase of the secondary higher harmonic components.
The technique described in the above-mentioned literature 1 uses the principle that the inductance of the PM motor is changed in accordance with the function of 2xcex8 for the phase xcex8 of the electrical angle. When the estimation of the positions of the magnetic poles is performed based on this principle, there may be a case that an error of 180xc2x0 is present with respect to the result of the estimation. If this state is maintained as it is, there is a possibility that the PM motor becomes uncontrollable at the time of starting the PM motor. Accordingly, it becomes necessary to provide means which discriminates the polarity of the magnetic pole axis (d axis) separately.
Further, the technique described in the literature 2, in the step 1, as in the case of the literature 1, performs the estimation of the positions of the magnetic poles by using the change of inductance to the electrical angle as in the case of the literature 1 in the step 1. In the step 2, a voltage step is generated on the PM motor and the polarity discrimination of the magnetic poles is performed based on a current response time at this point of time. The step 2 makes use of a phenomenon that the magnetic saturation is generated or decreased in response to the relationship between the magnetic flux generated by the permanent magnet and the magnetic flux component generated by the voltage step and eventually the inductance (electrical time constant) is changed. With the use of this technique, the discrimination of the polarities of the magnetic poles is possible and hence, it is possible to surely start the PM motor. However, this technique has a drawback that the estimation algorithm is divided in two stages (step 1, step 2) and hence, it takes some time to start the PM motor. Accordingly, it is difficult to apply such a technique to an application where a rapid acceleration is to be performed from a point of time that a power supply is turned on and the control algorithm also becomes complicated.
The technique described in the literature 3 estimates the polarities of the magnetic poles and the positions of the magnetic poles by applying the high frequency (approximately 500 Hz) to the PM motor and by extracting the distorted current components which are generated due to such an application of high frequency. Since the technique uses the phenomenon that the distortion of the waveform is derived from the magnetic saturation, the estimation of the positions of the magnetic poles can be performed without performing the discrimination of the polarities of the magnetic poles. However, it is necessary to accurately extract the high-frequency distortion components and hence, the fine sampling of the electric-current waveforms becomes necessary. Further, the technique requires the complicate processing such as the Fourier series or the Fourier expansion. To increase the accuracy of the Fourier series or the Fourier expansion, the detection of current for a reasonably long time is necessary and it takes some time to start the PS motor.
The present invention has been made in view of the above-mentioned drawbacks of the prior art and it is an object of the present invention to provide a driving system of an AC motor which is applicable to an electrically non-salient motor and can perform the determination of polarities and the detection of the position of magnetic poles with a simple algorithm.
The gist of the present invention which is provided for achieving the above-mentioned object lies in that, in the inside of a controller which controls a motor, the discrimination of polarities of magnetic poles and the detection of the positions of magnetic poles are performed or the detection of the positions of the magnetic poles are performed including the discrimination of magnetic poles and a vector control is performed.
The discrimination of the polarities is performed such that a minute voltage change is given to a dc axis which is an estimation axis of a magnetic flux in the inside of the motor, with respect to ripple components contained in observed values of a current which flows in the motor, current flow times at a positive side and a negative side of the ripple components are measured, and the polarities of magnetic poles in the inside of the motor are discriminated based on these values. Alternatively, the current change rates at the positive side and the negative side of the ripple components are measured and the polarities of magnetic poles are discriminated based on these values.
Here, the detection of the positions of the magnetic poles is performed such that in parallel with the above-mentioned discrimination of polarities of the magnetic poles, the electric current which flows in the motor is observed in a qc axis which is perpendicular to the dc axis and the estimation of the positions of the polarities in the inside of the motor is performed using the change-rate components of the observed current.
Another detection of the positions of the magnetic poles according to the present invention is performed such that a minute voltage change is given to voltage commands on the dc axis which is the estimation magnetic flux axis of the motor and to voltage commands on the qc axis which is perpendicular to the dc axis, the current which flows in the motor is observed on the dc axis and the qc axis, with respect to ripple components contained in the current values observed on the dc axis and the qc axis, the positions of the magnetic poles in the inside of the motor are estimated based on the current flow times at the positive side and the negative side of the ripple components. Alternatively, the current change rates of the ripple components are detected such that they are separately detected at the positive side and the negative side of the ripple components and, thereafter, the positions of the magnetic poles in the inside of the motor are estimated based on these change-rate values.
The estimation of the positions of the magnetic poles and the discrimination of the polarities may be performed in parallel and, upon the completion of the discrimination of the polarities, the cycle of the minute voltage change given to the voltage commands may be changed and thereafter the estimation of the positions of the magnetic poles may be performed in a succeeding manner.
Further, with respect to respective change rates of the current ripple components on the dc axis and the qc axis, that is, the change rate xcex94Idcp (the current change rate at the positive side of the ripple components of the dc-axis current), the change rate xcex94Idcn (the current change rate at the negative side of the ripple components of the dc-axis current), the change rate xcex94Iqcp (the current change rate at the positive side of the ripple components of the qc-axis current), the change rate xcex94Iqcn (the current change rate at the negative side of the ripple components of the qc-axis current), an axial error xcex94xcex8(=xcex8cxe2x88x92xcex8) which is the difference between a phase xcex8c of an electrical angle at the dc axis and the qc axis and a phase xcex8 of an magnetic pole axis in the inside of the motor is calculated based on an equation (10) explained later.
Alternatively, the positions of the magnetic poles are estimated based on the change of the inductance. That is, with respect to the current change rates at the separate positive and negative sides of the ripple components on the dc axis and the qc axis, the inverse numbers of the current change rates of respective axes and respective signs are calculated and the positions of the magnetic poles (the positions of the magnetic poles including polarites) in the inside of the motor are estimated based on these values. The inverse numbers of the current flow rates are proportional to the inductance.
Here, the inverse numbers of the positive and negative current change rates are Lmdcp (=1/|xcex94Idcp |), Lmdcn (=1/|xcex94Idcn|), Lmqcp (=1/|xcex94Iqcp |) and Lmqcn (=1/|xcex94Iqcn |) and the above-mentioned axial error xcex94xcex8(=xcex8cxe2x88x92xcex8) which is the difference between the phase xcex8c of the electrical angle at the dc axis and the qc axis and the phase xcex8 of the magnetic pole axis of the motor is calculated based on an equation (13) explained later.
According to the AC motor driving system of the present invention which has been explained above, it is possible to obtain an advantageous effect that by applying the minute voltage changes to the motor, the polarities of the magnetic poles in the inside of the motor can be easily discriminated based on the current flow times or the current change rates at the positive side and the negative side of the current ripple components which are generated by the application of the minute voltage changes.
Further, the detection of the positions of the magnetic poles can be performed using the known method or the method of the present invention in parallel with the discrimination of the polarities and hence, an advantageous effect that the time necessary for starting the motor can be shortened. By changing the cycle of the minute voltage change upon the completion of the discrimination of the polarities, the higher harmonics in current which are generated along with the estimation of the positions of the magnetic poles can be suppressed.
According to the AC motor driving system of the present invention, the minute voltage changes are given to the voltage commands on the dc axis and on the qc axis which is perpendicular to the dc axis and the positions of the magnetic poles are estimated based on the current flow times at the positive side and the negative side of the respective ripple current components. In this manner, the change of the ripple components due to the saturation of the motor is used and hence, the estimation of the positions of the magnetic poles including the polarities of the magnetic poles can be realized.
Alternatively, by performing the calculation with the use of the arc tangent function as a function relating to the current change rates of the ripple components, the axial error xcex94xcex8 between the control axis and the magnetic pole axis of the motor can be directly calculated and hence, the detection of the positions of the magnetic poles can be realized with a simple algorithm.
Further, with respect to the separate positive and negative current change rates of the current ripple components, the inverse numbers of these values are calculated and hence, the positions of the magnetic poles can be estimated based on the change of the inductance of the motor so that the estimation of the positions of the magnetic poles can be realized with high accuracy.